To be "sneaky" means to be trying to be undetected or unnoticed. To be "sly" means to be able to carry out activities without drawing attention to oneself. Given how similar these words are in meaning, they are synonyms. 

"Auspicious" is an adjective that can mean either "conducive to success; favorable," or "giving or being a sign of future success." So, we need to pick out an answer choice that is an adjective and means something like "favorable." So, "ominous" cannot be the correct answer because "ominous" means "giving the impression that something bad or unpleasant is going to happen; threatening; inauspicious," so "ominous" is an antonym of "auspicious." "Promising," however, is an adjective that means "showing signs of future success," and because it is the answer choice closest in meaning to "auspicious," "promising" is the correct answer.

"Precise" means marked by exactness, as in the sentence, "In order for the science experiment to work, we must make very precise measurements." "Exact" is most similar in meaning to "precise," so "exact" is the correct answer.

Incorrect answers:

"Perfect" is not the best answer because although you might describe precise measurements as being "perfect," the word "perfect" means as good as it is possible to be. For example, you might say "That was a perfect book report" or "I got a perfect score on my test." So, "exact" is close in meaning to "precise" than "perfect" is.

"Interesting" means holding or catching attention, as in the sentence, "The museum display of brightly colored butterflies was interesting to the students."

"Formal" means following accepted conventions or rules, as in the sentence, "My teacher's first name is Susan, but we address her formally as Mrs. Brown."

"Convoluted" is an adjective that means "extremely complex and difficult to follow" and is used of arguments, stories, or sentences. So, neither "simple" nor "straightforward" can be the correct answer because each of these words are antonyms of "convoluted," not synonyms. "Complex," however, is an adjective that means "consisting of many different and connected parts" or "not easy to analyze or understand; complicated or intricate." Because it is the answer choice closest in meaning to "convoluted," "complex" is the correct answer.

The adjective "intricate" refers to something that is complex or nuanced. It is sometimes used to describe physical complexity (like an intricate system of highways), but also applies to ideas that may be difficult to grasp. "Complicated" is the clear synonym here. Of the remaining choices, both "straightforward" and "simple" are antonyms of the given word, since they convey a lack of complexity. "Unified" is used to describe groups that have been united or brought together.

The adjective "precise" refers to an extremely accurate or specific measurement or assessment. "Exact," which also refers to an accurate or correct quantity, is our answer. "Careless" is clearly incorrect, since it describes something that is sloppy and unlikely to be perfectly measured. You might use the word "immature" to describe a person who acts unusually young and inexperienced; neither this term nor "incomplete" (unfinished) is related to the given word.

Both enchanting and delectable can be defined as highly pleasing. 

Discouraging, dueling, and dreadful are antonyms to enchanting.

Something enchanting may or may not be confusing, so that does not work either.

"Heinous" means shockingly evil. "Benign" means harmless, while "generous" means giving, and "benevolent" means good. If you can figure out that "benign," "generous," and "benevolent" all have similar meanings and are not synonyms of "heinous," you can narrow down the answer to "evil."

"Contrary" means opposite or willfully refusing to agree, so "opposite" is the correct answer. You can also figure this out by thinking of the phrase "on the contrary," which is used to introduce information that considers the topic of conversation from an opposing viewpoint. None of the other answer choices are close in meaning to "contrary": "cooperative" means working together toward a common goal; "stubborn" means refusing to change one's mind even when given good evidence or reasons to do so; and "wary" means cautious or careful.

The word "ominous" means threatening or suggesting that something bad is going to happen; therefore, "menacing," which also means threatening, is the word that most closely matches the definition of "ominous." "Auspicious," which means favorable or promising, is the opposite of "ominous," and therefore incorrect. "Sorrowful," which means feeling or showing sadness, and "obnoxious" are unrelated to the definition of "ominous" and therefore also incorrect.